Volatile sulfur compounds, which are generated from drain outlets or waste such as kitchen garbage, are malodorous components which give unpleasant feelings to people even at low concentration. These volatile sulfur compounds are generated through decomposition of a sulfur-containing amino acid such as cysteine and methionine or a protein containing it in sewage, waste, or the like by the action of a metabolizing enzyme such as methionine lyase and cysteine lyase possessed by bacteria. Among volatile sulfur compounds responsible for unpleasant odors, for example, methylmercaptan is formed from methionine by the action of methionine lyase, and hydrogen sulfide is formed from cysteine by the action of cysteine lyase. Further, from methylmercaptan or hydrogen sulfide, sulfide compounds including dimethyl sulfide, dimethyl disulfide, and dimethyl trisulfide are enzymatically or oxidatively formed, and they are also responsible for malodors.
Patent Literature 1 discloses addition of a fragrance component as a deodorizer or an aromatic agent to a composition for washing, sterilization, anti-staining, or deodorization for drain outlets or the like. Patent Literature 2 discloses that a particular fragrance component inhibits the action of an enzyme to form methylmercaptan from methionine or an enzyme to form hydrogen sulfide from cysteine to suppress malodors caused by volatile sulfur compounds generated from waste, drain outlets, etc.
Mammals including humans recognize a smell through the mechanism in which a smell molecule binds to an olfactory receptor (OR) on an olfactory sensory neuron present in the olfactory epithelium in the upper part of the nasal cavity, and the response of the receptor thereto is transmitted to the central nerve system. For humans, it has been reported that approximately 400 olfactory receptors are present, and genes encoding them account for approximately 2% of the total genes of a human. In general, olfactory receptors and smell molecules are associated in many-to-many relationship. That is, an individual olfactory receptor receives a plurality of structurally similar smell molecules at different affinities, and an individual smell molecule is received by a plurality of olfactory receptors. In addition, it has been reported that a smell molecule which activates an olfactory receptor functions as an antagonist to inhibit the activation of another olfactory receptor. Combination of the responses of a plurality of olfactory receptors provides recognition of an individual smell.
Accordingly, the receptor response to one smell molecule may be inhibited by another smell molecule concomitantly present, which ultimately results in that a completely different smell is recognized. This mechanism is called olfactory receptor antagonism. In contrast to deodorization by addition of another smell of a perfume, an aromatic agent, or the like, the suppression of a smell through the receptor antagonism can specifically disable recognition of a particular malodor, and has an advantage that unpleasant feelings due to a smell of an aromatic agent are not caused.
On the basis of the concept of the olfactory receptor antagonism, several methods for identifying malodor-suppressing substances by using the activity of an olfactory receptor as an indicator have been previously disclosed. For example, Patent Literatures 3 and 4 disclose searching for substances which suppress malodors of hexanoic acid, skatole, etc., by using, as an indicator, the activity of an olfactory receptor specifically responsive to the malodor substances. Patent Literature 5 discloses searching for substances which suppress sweat odor by using, as an indicator, the activity of an olfactory receptor responsive to a particular carboxylic acid(s). Patent Literature 6 discloses a method of identifying agents capable of regulating the function of a polypeptide encoding an olfactory receptor through measurement of the activity of the polypeptide in the presence of isovaleric acid or an equivalent thereof. Patent Literature 7 discloses a method of screening a library of chemical substances for compounds relating to sense of smell through identification of compounds which specifically bind to a polypeptide encoding an olfactory receptor.
However, a technique to suppress malodors of the above-mentioned volatile sulfur compounds generated from waste, drain outlets, or the like on the basis of the olfactory receptor antagonism has not been reported yet.    Patent Literature 1: JP-A-2006-206882    Patent Literature 2: JP-A-2010-004971    Patent Literature 3: JP-A-2012-050411    Patent Literature 4: JP-A-2012-249614    Patent Literature 5: US 2013/0336910 A1    Patent Literature 6: WO 2006/094704    Patent Literature 7: JP-A-2004-504010